(1) Field of the Invention
The present invention relates to a substrate transport apparatus for fetching substrates, one at a time, from cassettes storing the substrates, such as semiconductor wafers or glass substrates for liquid crystal displays, in multiple stages, transporting the fetched substrates to a substrate cleaning section for cleaning with pure water or the like, and transporting cleaned substrates back into the cassettes. The apparatus supports the substrates by vacuum suction during the transport between the cassettes arranged on a base for storing the substrates in multiple stages, and the substrate cleaning section for cleaning the substrates. The substrates are fetched from the cassettes, transported to the substrate cleaning section, and transported back into the cassettes after a cleaning treatment in the substrate cleaning section.
(2) Related Art Statement
Preferably, the substrates are stored in each cassette with a narrow vertical space between adjacent substrates so that the cassette may hold a large number of substrates. It is difficult for a substrate transport apparatus as noted above to employ a pin-support type substrate holding device for entering such a narrow space and supporting each substrate through point contacts. Generally, therefore, a substrate transport device having a thin, vacuum type suction arm is used for transporting the substrates into and out of the cassettes. The suction arm is moved to a position under one of the substrates stored in multiple stages in one of the cassettes. The substrate is placed on and drawn by vacuum suction to an upper surface of the suction arm. The substrate is brought out of the cassette in this state, and transferred to a pin-support type position adjusting mechanism waiting at a standby position. After a position adjustment, the substrate is delivered to an edge-holding type substrate transport device for processing. This process substrate transport device transports the substrate to the cleaning section. After a cleaning treatment, the substrate is transported by the process transport device and delivered to the position adjusting mechanism. After a position adjustment, the cleaned substrate is transported by the cassette-side transport device to a position opposed to a selected one of the cassettes, and then deposited in that cassette. (see Japanese Patent Application No. 2-137490)
With the conventional substrate transport apparatus, however, the same suction arm that carries substrates yet to be cleaned in fetching them from the cassettes is used also for depositing cleaned substrates in the cassettes. When the substrates are fetched from the cassettes, particles adhering to lower surfaces of the substrates are transferred to a supporting surface of the suction arm. Since the same suction arm is used to deposit cleaned substrates in the cassettes, lower surfaces of the cleaned substrates become recontaminated to deteriorate product quality.
Only a low yield is secured particularly where such a substrate transport apparatus is used in the type of substrate cleaning machine that cleans both upper and lower surfaces of substrates. Thus, improvement has been desired.